Method and apparatus for providing wireless charging power to a wireless power receiver

ABSTRACT

A control method of a wireless power transmitter and a wireless power transmitter. The method includes transmitting a first power with a first cycle; transmitting a second power with a second cycle, wherein the second cycle is greater than the first cycle; when a wireless power receiver is placed within a charging area and is detected by the first power, upon detecting the wireless power receiver by the first power, transmitting a third power to drive the wireless power receiver to transmit a search signal to the wireless power transmitter; and when the wireless power receiver is placed within the charging area and is not detected by the first power, using the second power to detect the wireless power receiver and drive the wireless power receiver to transmit the search signal to the wireless power transmitter.

PRIORITY

This application is a continuation of U.S. application Ser. No.15/945,378, filed Apr. 4, 2018, which is a continuation applicationclaiming priority under 35 U.S.C. § 120 to U.S. patent application Ser.No. 13/937,793, filed on Jul. 9, 2013, now U.S. Pat. No. 9,966,802. inthe United States Patent and Trademark Office, which claims priorityunder U.S.C. § 119(a) to Korean Patent Application Serial Nos.10-2012-0074492 and 10-2012-0082278, which were filed in the KoreanIntellectual Property Office on Jul. 9, 2012 and Jul. 27, 2012,respectively, the entire disclosure of each of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a wireless power transmitterand method of controlling the same, and more particularly, to a wirelesspower transmitter and method for transmitting wireless charging power toa wireless power receiver.

2. Description of the Related Art

Mobile terminals, such as cell phones, Personal Digital Assistants(PDAs), etc., are powered by rechargeable batteries, which are rechargedwith electric energy provided using separate charging devices. Forexample, for a charging device and a battery having contacting terminalson their outer surfaces, the battery is electrically connected to thecharging device by having their contacting terminals contact each other.However, when using such a contact charging method, the contactingterminals are susceptible to contamination by dirt or corrosion whenexposed to moisture because they are exposed on the outer surfaces ifthe charging device and the battery. Obviously, any contamination orcorrosion will negatively affect charging.

To address this problem, wireless charging or contactless chargingtechnologies have been developed.

Wireless charging technology uses wireless power transmission andreception. For example, a battery of a cell phone can be wirelesslycharged merely by placing the cell phone on a charging pad, withoutconnecting or plugging in a separate charging connector. Wirelesscharging technology is commonly applied to electric toothbrushes orshavers.

There are a number of different wireless charging technologies, i.e., anelectromagnetic induction method using coils, a resonance method usingresonance, and a Radio Frequency (RF)/micro wave radiation method thatconverts electric energy into microwaves for transmission.

The electromagnetic induction method transfers power between primary andsecondary coils. Specifically, moving a magnet through a coil producesan induced current from which a magnetic field is produced at atransmission end, and the change in the magnetic field at a receivingend induces a current to generate energy therein. This phenomenon iscommonly referred to as magnetic induction, and a power transmissionmethod based on magnetic induction provides superior energy transmissionefficiency.

The resonance method uses a resonance-based power transmission principlebased on the Coupled Mode Theory, i.e., a physical concept that a tuningfork being placed next to a wine glass causes the wine glass to ringwith the same frequency. However, in resonance-based power transmission,resonated electromagnetic waves carry electric energy, instead ofresonating sound. Resonant electric energy of the electromagnetic wavesis directly transferred to a device having the same resonant frequency,and the non-used part of the energy is re-absorbed into the magneticfield rather than being dispersed in the air. As a result, resonantelectric energy is not deemed harmful to surrounding machines or bodies.

Although various studies on wireless charging methods have been done,standards for prioritizing wireless charging, searching for wirelesspower transmitters/receivers, selecting a communication frequencybetween a wireless power transmitter and receiver, adjusting wirelesspower, selecting a matching circuit, distributing communication time foreach wireless power receiver in a single charging cycle, etc., have notbeen provided. In this regard, a need exists for standardizationrelating to a method of detecting wireless power receivers by a wirelesspower transmitter.

SUMMARY OF THE INVENTION

The present invention is designed to address at least the problemsand/or disadvantages described above and to provide at least theadvantages described below.

Accordingly, an aspect of the present invention is to provide a standardfor general operations of a wireless power transmitter.

Another aspect of the present invention is to provide a structure andprocess for detecting a wireless power receiver by a wireless powertransmitter.

In accordance with an aspect of the present invention, a control methodof a wireless power transmitter is provided. The method includestransmitting a first power with a first cycle; transmitting a secondpower with a second cycle, wherein the second cycle is greater than thefirst cycle; when a wireless power receiver is placed within a chargingarea and is detected by the first power, upon detecting the wirelesspower receiver by the first power, transmitting a third power to drivethe wireless power receiver to transmit a search signal to the wirelesspower transmitter; and when the wireless power receiver is placed withinthe charging area and is not detected by the first power, using thesecond power to detect the wireless power receiver and drive thewireless power receiver to transmit the search signal to the wirelesspower transmitter.

In accordance with another aspect of the present invention, a wirelesspower transmitter is provided. The wireless power transmitter includes aresonator; and a controller configured to control to transmit a firstpower with a first cycle through the resonator, control to transmit asecond power with a second cycle through the resonator, wherein thesecond cycle is greater than the first cycle, when a wireless powerreceiver is placed within a charging area and is detected by the firstpower, upon detecting the wireless power receiver by the first power,control to transmit a third power to drive the wireless power receiverto transmit a search signal to the wireless power transmitter, throughthe resonator, and when the wireless power receiver is placed within thecharging area and is not detected by the first power, control to use thesecond power to detect the wireless power receiver and drive thewireless power receiver to transmit the search signal to the wirelesspower transmitter.

In accordance with another aspect of the present invention, a controlmethod of a wireless power transmitter is provided. The method includestransmitting a first power with a first cycle; transmitting a secondpower with a second cycle, wherein the second cycle is greater than thefirst cycle; in response to detecting that a wireless power receiver isplaced within a charging area while transmitting the first power,transmitting a third power to drive the wireless power receiver totransmit a search signal to the wireless power transmitter; and inresponse to detecting that the wireless power receiver is placed withinthe charging area while transmitting the second power, maintaining totransmit the second power to drive the wireless power receiver totransmit the search signal to the wireless power transmitter.

In accordance with another aspect of the present invention, a wirelesspower transmitter is provided. The wireless power transmitter includes aresonator; and a controller configured to control to transmit a firstpower with a first cycle through the resonator, control to transmit asecond power with a second cycle through the resonator, wherein thesecond cycle is greater than the first cycle, in response to detectingthat a wireless power receiver is placed within a charging area whiletransmitting the first power, control to transmit a third power to drivethe wireless power receiver to transmit a search signal to the wirelesspower transmitter, through the resonator, and in response to detectingthat the wireless power receiver is placed within the charging areawhile transmitting the second power, maintain to transmit the secondpower to drive the wireless power receiver to transmit the search signalto the wireless power transmitter, through the resonator.

In accordance with another aspect of the present invention, a controlmethod of a wireless power transmitter is provided. The method includestransmitting a first power during a first duration; after apredetermined duration after transmitting the first power, transmittinga second power during a second duration, wherein the first duration isless than the second duration; in response to detecting that a wirelesspower receiver is placed within a charging area while transmitting thefirst power, transmitting a third power to drive the wireless powerreceiver to transmit a search signal to the wireless power transmitter;and in response to detecting that the wireless power receiver is placedwithin the charging area while transmitting the second power,maintaining to transmit the second power to drive the wireless powerreceiver to transmit the search signal to the wireless powertransmitter.

In accordance with another aspect of the present invention, a wirelesspower transmitter is provided. The wireless power transmitter includes aresonator; and a controller configured to control to transmit a firstpower during a first duration through the resonator; after apredetermined duration after transmitting the first power, control totransmit a second power during a second duration through the resonator,wherein the first duration is less than the second duration, in responseto detecting that a wireless power receiver is placed within a chargingarea while transmitting the first power, control to transmit a thirdpower to drive the wireless power receiver to transmit a search signalto the wireless power transmitter, through the resonator, and inresponse to detecting that the wireless power receiver is placed withinthe charging area while transmitting the second power, maintain totransmit the second power to drive the wireless power receiver totransmit the search signal to the wireless power transmitter, throughthe resonator.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will become more apparent from thefollowing description thereof with reference to the attached drawings,in which:

FIG. 1 illustrates a wireless charging system according to an embodimentof the present invention;

FIG. 2A is a block diagram illustrating a wireless power transmitter anda wireless power receiver, according to an embodiment of the presentinvention;

FIG. 2B is a block diagram illustrating a wireless power receiver,according to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating a method of controlling a wirelesspower transmitter/receiver, according to an embodiment of the presentinvention;

FIG. 4 illustrates a conventional method of detecting a wireless powerreceiver;

FIG. 5 illustrates a conventional method of detecting a wireless powerreceiver;

FIG. 6 illustrates a method of detecting a wireless power receiver,according to an embodiment of the present invention;

FIG. 7 illustrates a method of detecting a relatively small wirelesspower receiver, according to an embodiment of the present invention;

FIG. 8 is a flowchart illustrating a method of controlling a wirelesspower transmitter, according to an embodiment of the present invention;

FIG. 9 illustrates a method of detecting a wireless power receiver,according to an embodiment of the present invention;

FIG. 10 illustrates method of detecting a relatively small wirelesspower receiver, according to an embodiment of the present invention;

FIG. 11 is a flowchart illustrating a method of controlling a wirelesspower transmitter, according to an embodiment of the present invention;

FIG. 12 illustrates a method of detecting a wireless power receiver,according to an embodiment of the present invention; and

FIGS. 13A to 13C are diagrams illustrating detected power applied by awireless power transmitter, according to various embodiments of thepresent invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, specific details such as detailed configuration andcomponents are merely provided to assist the overall understanding ofthese embodiments of the present invention. Therefore, it should beapparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the present invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

FIG. 1 illustrates a wireless charging system according to an embodimentof the present invention.

Referring to FIG. 1, the wireless charging system includes a wirelesspower transmitter 100 and wireless power receivers 110-1, 110-2, and110-n. For example, the wireless power receivers 110-1, 110-2, and 110-nmay be implemented in mobile communication terminals, Personal DigitalAssistants (PDAs), Portable Multimedia Players (PMPs), smartphones, etc.

The wireless power transmitter 100 wirelessly transmits powers 1-1, 1-2,and 1-n to the wireless power receivers 110-1, 110-2, and 110-n, whichare authenticated via a predetermined authentication procedure.

The wireless power transmitter 100 makes an electrical connection withthe wireless power receivers 110-1, 110-2, and 110-n. For example, thewireless power transmitter 100 transmits wireless power to the wirelesspower receivers 110-1, 110-2, and 110-n in an electromagnetic waveform.

The wireless power transmitter 100 also performs bidirectionalcommunication with the wireless power receivers 110-1, 110-2, and 110-n.The wireless power transmitter 100 and the wireless power receivers110-1, 110-2, 110-n process and transmit/receive packets 201, 202, and2-n, which include certain frames, which will be described in moredetail below.

The wireless power transmitter 100 provides the wireless power to thewireless power receivers 110-1, 110-2, and 110-n, e.g., based on aresonance method.

When the resonance method is used by the wireless power transmitter 100,a distance between the wireless power transmitter 100 and the wirelesspower receivers 110-1, 110-2, and 110-n may be 30 m or less. However,when an electromagnetic induction method is used by the wireless powertransmitter 100, a distance between the wireless power transmitter 100and the wireless power receivers 110-1, 110-2, and 110-n may be 10 cm orless.

Each of the wireless power receivers 110-1. 110-2, and 110-n charges abattery therein using the wireless power received from the wirelesspower transmitter 100. The wireless power receivers 110-1, 110-2, and110-n also transmit a signal to the wireless power transmitter 100,requesting the wireless power transmission, information for wirelesspower reception, information on a state of the wireless power receiver,control information of the wireless power transmitter, etc., which willbe described in more detail below.

The wireless power receivers 110-1, 110-2, and 110-n transmit a messageindicating a respective charging state to the wireless power transmitter100.

For example, the wireless power transmitter 100 may include a display,which displays the respective states of the wireless power receivers110-1, 110-2, and 110-n, based on the respective messages received fromthe wireless power receivers 110-1, 110-2, and 110-n. The wireless powertransmitter 100 may also display an estimate of a remaining time untilcompletion of the charging the respective wireless power receivers110-1, 110-2, and 110-n.

The wireless power transmitter 100 transmits a control signal to each ofthe wireless power receivers 110-1, 110-2, and 110-n to disable itswireless charging function. After receiving the control signal from thewireless power transmitter 100, the wireless power receivers 110-1,110-2, and 110-n disable their own wireless charging functions.

FIG. 2A is a block diagram illustrating a wireless power transmitter anda wireless power receiver, according to an embodiment of the presentinvention.

Referring to FIG. 2A, the wireless power transmitter 200 includes apower transmitter 211, a controller 212, and a communication unit 213,e.g., a transceiver. The wireless power receiver 250 includes a powerreceiver 251, a controller 252, and a communication unit 253, e.g., atransceiver.

The power transmitter 211 wirelessly transmits power to the wirelesspower receiver 250. Herein, the power transmitter 211 may supply thepower in an Alternating Current (AC) waveform, or may convert power in aDirect Current (DC) form into the AC waveform using an inverter (notshown).

The power transmitter 211 may be implemented as a built-in battery or asa power receiving interface that receives power from an outside source.A person having ordinary skill in the art will readily understand thatthe power transmitter 211 is not limited thereto, but may be implementedby another hardware device that provides power in an AC waveform.

In addition, the power transmitter 211 provides the AC waveform aselectromagnetic waves to the wireless power receiver 250, i.e., thepower receiver 251. For example, the power transmitter 211 may include aloop coil to transmit and receive the electromagnetic waves, whereininductance L of the loop coil may be variable.

The controller 212 controls general operations of the wireless powertransmitter 200. For example, the controller 212 may control the generaloperations of the wireless power transmitter 200 by using a controlalgorithm, a program, or an application read from a storage memory (notshown). The controller 212 may be implemented as a Central ProcessingUnit (CPU), a microprocessor, a mini-computer, etc.

The communication unit 213 communicates with the wireless power receiver250, i.e., the communication unit 253, in a predetermined communicationmethod. For example, the communication unit 213 communicates with thecommunication unit 253 of the wireless power receiver 250 using NearField Communication (NFC), Zigbee communication, infrared communication,ultraviolet communication, etc. More specifically, the communicationunit 213 may use the Institute of Electrical and Electronics Engineers(IEEE) 802.15.4 Zigbee communication method or the Carrier SenseMultiple Access with Collision Avoidance (CSMA/CA) algorithm.

The communication unit 213 transmits an information signal of thewireless power transmitter 200. For example, the communication unit 213may unicast, multicast, or broadcast the information signal.

Table 1 below shows an example of a data structure of the informationsignal transmitted from the wireless power transmitter 200. For example,the wireless power transmitter 200 may transmit the signal shown inTable 1 in predetermined intervals, wherein the signal is referred to asa notice signal.

TABLE 1 Frame Protocol Sequence Network RX to Report Number Type VersionNumber ID (schedule mask) Reserved of RX Notice 4 bits 1 byte 1 byte 1byte 5 bits 3 bits

In Table 1, the Frame Type field indicates a type of the signal, i.e., aNotice signal. The Protocol Version field indicates a type of a protocolof the communication method, and is assigned 4 bits. The sequence Numberfield indicates a sequential order of the corresponding signal, andassigned 1 byte. For example, the sequential order of the SequenceNumber may be incremented by 1 for each signal transmission orreception. The Network ID field indicates a network identifier of thewireless power transmitter 200, and is assigned 1 byte. The Rx to Report(schedule mask) field indicates the wireless power receiver that is toreport to the wireless power transmitter 200, and is assigned 1 byte.

Table 2 shows an example of the Rx to Report (schedule mask) field,according to an embodiment of the present invention.

TABLE 2 RX to Report (schedule mask) Rx1 Rx2 Rx3 Rx4 Rx5 Rx6 Rx7 Rx8 1 00 0 0 1 1 1

In Table 2, Rx1 to Rx8 correspond to wireless power receivers 1 to 8. Inthe Rx to Report (schedule mask) field shown in table 2, wireless powerreceivers with bit set to ‘1’, i.e., Rx1, Rx6, Rx7, and Rx8, shouldreport.

The Reserved field is reserved for later use, and is assigned 5 bytes.The Number of Rx field indicates the number of wireless power receiversaround the wireless power transmitter 200, and is assigned 3 bits.

The signal in Table 1 may be assigned to a Wireless Power Transfer (WPT)of a data structure in the IEEE 802.15.4 format. Table 3 shows the datastructure in the IEEE 802.15.4 format.

TABLE 3 Preamble SFD Frame Length WPT CRC16

In Table 3, the data structure in the IEEE 802.15.4 format includes aPreamble field, a Start Frame Delimiter (SFD) field, a Frame Lengthfield, a WPT field, a Cyclic Redundancy Check (CRC) 16 field, where thedata structure shown in Table 1 may correspond to the WPT field.

The communication unit 213 receives power information from the wirelesspower receiver 250. For example, the power information includes at leastone of a capacity of the wireless power receiver 250, remaining batterypower, frequency of charging, battery consumption, battery capacity, anda battery charge/consumption ratio. The communication unit 213 transmitsa charging function control signal to control a charging function of thewireless power receiver 250. The charge function control signal is acontrol signal to controls, i.e., turns on and off, the chargingfunction of the power receiver 251 of the wireless power receiver 250.

The communication unit 213 receives signals from the wireless powerreceiver 250 and from different wireless power transmitters (not shown).For example, the communication unit 213 receives a Notice signal asshown in Table 1 from a different wireless power transmitter. Thecontroller 252 controls overall operation of the wireless power receiver250.

Although FIG. 2A illustrates the wireless power transmitter 200 having aseparate power transmitter 211 and communication unit 213 and usingout-band communications, the wireless power transmitter 200 is notlimited thereto. For example, the power transmitter 211 and thecommunication unit 213 may be integrated in a single hardware device,and thus, the wireless power transmitter 200 may use in-bandcommunications.

FIG. 2B is a block diagram illustrating a wireless power receiver,according to an embodiment of the present invention.

Referring to FIG. 2B, the wireless power receiver 250 includes a powerreceiver 251, a controller 252, a communication unit 253, a rectifier254, a DC-to-DC converter 255, a switching unit 256, and a charging unit257. Because the power receiver 251, the controller 252, and thecommunication unit 253 have already been described above with referenceto FIG. 2A, the description of the power receiver 251, the controller252 and the communication unit 253 will be omitted here.

The rectifier 254, e.g., bridge diodes, rectifies the wireless powerreceived by the power receiver 251 into a DC format. The DC-to-DCconverter 255 converts the rectified power with a predetermined gain.For example, the DC-to-DC converter 255 converts the rectified voltageto 5V at its output end 259. However, minimum and maximum values of avoltage to be applied to the front end (input end) 258 of the DC-to-DCconverter 255 may be preset, and the values may be recorded in InputVoltage MIN and Input Voltage MAX fields of a request join signal,respectively, which will be discussed in more detail below.

Rated voltage and rated current at the output end 259 of the DC-to-DCconverter 255 may also be recorded in Typical Output Voltage and TypicalOutput Current fields of the request join signal.

The switching unit 256 connects the DC-to-DC converter 255 to thecharging unit 257. The switching unit 256 keeps an ON or OFF state,under control of the controller 252. The charging unit 257 stores theconverted power input from the DC-to-DC converter 255, when theswitching unit 256 is in the ON state.

FIG. 3 is a flowchart illustrating a method of controlling a wirelesspower transmitter/receiver, according to an embodiment of the presentinvention.

Referring to FIG. 3, the wireless power transmitter detects a nearbyobject in step S301. For example, the wireless power transmitter maydetermine whether there is a new object in proximity to the wirelesspower transmitter by detecting a load change or based on other criteria,such as voltage, current, phase, temperature, etc.

In step S303, the wireless power receiver searches for wireless powertransmitters on at least one channel, to determine a wireless powertransmitter from which to receive wireless power. For example, thewireless power receiver sends a signal to search for at least onewireless power transmitter to the at least one wireless powertransmitter and determines a wireless power transmitter from which toreceive wireless power, based on received response signals to the signalto search for at least one wireless power transmitter. The wirelesspower receiver then pairs with the wireless power transmitter from whichto receive wireless power.

The wireless power receiver may subscribe to a wireless power networkcontrolled by the wireless power transmitter from which to receive thewireless power. For example, the wireless power receiver may transmit asubscription request signal to the wireless power transmitter from whichto receive the wireless power. In return, the wireless power receiverreceives a subscription response signal from the wireless powertransmitter. For example, the subscription response signal includesinformation about whether or not the subscription is allowed.Accordingly, wireless power receiver determines whether it subscribes tothe wireless power network using the subscription response signal.

In step S307, the wireless power transmitter from which to receive thewireless power and the wireless power receiver enter a standby mode. Inthe standby mode, the wireless power transmitter transmits a commandsignal to the wireless power receiver. The wireless power receivertransmits a report signal or acknowledgment (ACK) signal in response tothe command signal. If the command signal includes a command to initiatecharging, the wireless power receiver may initiate charging, in stepS309.

FIG. 4 illustrates a conventional method of detecting a wireless powerreceiver.

Referring to FIG. 4, a wireless power transmitter 1101 remains in adetecting state, wherein it transmits the detection power Pdet 1110 and1111, during an effective duration tdet for each predetermined cycletdetper. The detection power Pdet 1110 and 1111, and the effectiveduration tdet are determined based on a minimum power and time requiredfor the wireless power transmitter 1101 to detect whether there is acandidate device for wireless charging within an effective range bydetecting a load change of the power transmitter, i.e., a load change ofa resonator. That is, because a candidate device, i.e., a metal object,is detected by a load change of the resonator, the wireless powertransmitter 1101 may minimize power consumption in the detection stateby periodically generating a sine wave having a relatively low voltage,but still capable of detecting the load of the resonator for asufficient time to detect the load. The detection state is maintaineduntil a new device is detected during the effective duration tdet.

For example, when a wireless power receiver is located over the wirelesspower transmitter 1101, the wireless power transmitter 1101 may detectthe load change and determine that an object is nearby. Although FIG. 4describes that the wireless power transmitter 1101 detects a nearbyobject based on a load change, the wireless power transmitter 1101 maydetect a nearby object based on other criteria, such as a voltagechange, a current change, a temperature change, a phase change, etc.

When the wireless power receiver 1102 is placed adjacent to the wirelesspower transmitter 1101, the wireless power transmitter 1101 detects theload change when transmitting the detection power Pdet 1111.

Upon detecting an object, i.e., the wireless power receiver 1102, in theeffective detection duration tdet, the wireless power transmitter 1101then transmits driving power Preg 1114. Here, the driving power 1114 hasa sufficient power level to drive a controller or an MCU of the wirelesspower receiver 1102. The wireless power receiver 1102 transmits a searchsignal 1112, and the wireless power transmitter 1101 responds to thewireless power receiver 1120 with a response search signal 1113.

As described above, the conventional wireless power transmitter 1101applies the detection power periodically to detect a wireless powerreceiver. However, when a wireless power receiver has relatively lowpower consumption, the wireless power transmitter 1101 may not detectthe wireless power receiver, because the low power consumption may notcause a significant enough load change to be detected. In this case, theload change of the wireless power transmitter 1101 is notdistinguishable from noise. Thus, the conventional wireless powertransmitter 1101 will not detect the wireless power receiver.

FIG. 5 illustrates a conventional method of detecting a wireless powerreceiver.

Referring to FIG. 5, the conventional wireless power transmitter 1001remains in the detecting state, wherein the detection powers Pbea 1041and 1051 are transmitted during an effective detection duration tbea foreach predetermined cycle tea_per. The detection power Pbea 1041 and 1051drives a wireless power receiver and the effective detection durationtbea is a time for which to drive the wireless power receiver andconduct certain communication.

For example, when a wireless power receiver 1002 is placed over awireless power transmitter 1001, as at time 1003, the wireless powertransmitter 1001 detects a load change and determines that an object islocated nearby. Although FIG. 5 is described with the wireless powertransmitter 1001 detecting a nearby object based on a load change, thewireless power transmitter 1001 may also detect the nearby object basedon other criteria, such as a voltage change, a current change, atemperature change, a phase change, etc.

When the wireless power receiver 1002 is placed over the wireless powertransmitter 1001, i.e., at time 1003, the wireless power transmitter1001 detects the load change within the next time tbea for which totransmit the detection power Pbea 1061.

Further, after detecting an object, i.e., the wireless power receiver1002, in the effective detection duration, the wireless powertransmitter 1001 keeps applying the detection power 1061.

As described above, the conventional wireless power transmitter 1001 inFIG. 5 applies the detection power periodically to detect the wirelesspower receiver 1002. However, the conventional wireless powertransmitter 1001 continues to transmit power to drive the wireless powerreceiver 1002, while the wireless power receiver 1002 is driven and ableto conduct communication, thereby wasting power.

FIG. 6 illustrates a method of detecting a wireless power receiver,according to an embodiment of the present invention.

Referring to FIG. 6, a wireless power transmitter 600 applies differentkinds of detection power during a predetermined cycle (referred toherein as a “beacon cycle”). The beacon cycle includes first and secondperiods of time. Specifically, the wireless power transmitter 600applies a first detection power 601 for the first period of time andsecond detection powers 602 to 610 for the second period of time. Thewireless power transmitter 600 applies the first detection power 601 fora time of L ms.

The first detection power 601 is strong enough to drive a wireless powerreceiver. For the time of the L ms for which the first detection power601 transmitted, the wireless power receiver is driven and cancommunicate. Each of the second detection powers 602 to 610 have asufficient power level to detect a wireless power receiver. Each of thesecond detection powers has a cycle of N ms. The gap between pieces ofthe second detection powers may be a time of (N−K) ms.

When the beacon cycle is over, the wireless power transmitter 600applies the first detection power 611 again.

The wireless power transmitter 600 also uses the second detection powers612 to 615.

Herein, it is assumed that a wireless power receiver 650 is placed overthe wireless power transmitter 600 between applying the second detectionpowers 614 and 615. If the wireless power receiver 650 has relativelyhigh power consumption, the wireless power transmitter 600 will detect aload change during the application of the second detection power 615,based on the load change.

After detecting the wireless power receiver 650, the wireless powertransmitter 600 applies driving power 616, which drives the controlleror an MCU of the wireless power receiver 650.

The wireless power receiver 650 receives the driving power 616. Thewireless power receiver 650 generates and transmits a signal to searchfor a wireless power transmitter (hereinafter, referred to as a “searchsignal”), based on the received driving power 616.

The search signal is used to search for a wireless power transmitterfrom which to receive the wireless power, and may have a data structureas shown in Table 4, below.

TABLE 4 Frame Protocol Sequence Company Product power Type VersionNumber ID ID Impedance category consumption Search 4 bits 1 bye 1 byte 4bytes 4 bits 4 bits 4 bits

In Table 4, the Frame Type field indicates a type of the signal, i.e., asearch signal. The Protocol Version field indicates a type of a protocolof the communication method, and is assigned 4 bits. The Sequence Numberfield indicates a sequential order of the signal, and is assigned 1byte. For example, the sequential order of the Sequence Number may beincremented by 1 for each signal transmission or reception.

Specifically, if the Sequence Number of the notice signal of Table 1 is‘ 1’, then the search signal's Sequence Number may be ‘2’.

The Company ID field has information about a manufacturer of thewireless power receiver, and is assigned e.g., 1 byte. The Product IDfield has product information of the wireless power receiver, e.g.,serial number information. The Product ID is assigned 4 bytes.

The Impedance field has impedance information of the wireless powerreceiver, and is assigned 4 bits. In the Impedance field, impedanceinformation of the receiving resonator may be written.

The Category field has rated-power information or size information ofthe wireless power receiver, and is assigned 4 bits. The PowerConsumption field has power loss information estimated by the wirelesspower receiver, and is assigned 4 bits. Each or a sum of power loss(PRX-COIL) in the receiving resonator, power loss (PINDUCTION) due tothe mutual inductance of the transmitting resonator and the receivingresonator, power loss (PREC) in a rectifier of the wireless powerreceiver may be written in the Power Consumption field. Additionally,voltage and current at the input end of a DC-to-DC converter of thewireless power receiver may also be written in the Power Consumptionfield.

The wireless power transmitter may manage related information of eachwireless power receiver based on the input search signal. Table 5 is anexample of a device control table, according to an embodiment of thepresent invention.

TABLE 5 Session company Product Load Current Voltage efficiency statusinput output output ID ID ID Characteristic Characteristiccharacteristic characteristic characteristic voltage voltage current 10x11111111 0x11111111 25 300 mA 5 V 75% complete & — 5 V 300 mA standby2 0x22222222 0x11111111 30 500 mA 3 V 70% Charge(CV) 3 V 3 V 400 mA 30x33333333 0x22222222 10 100 mA 5 V 80% charge(CC) 5 V 5 V 100 mA 40x44444444 0x11111111 50 500 mA 5 V 75% Charge(CC) 5 V 5 V 500 mA 50x55555555 0x33333333 100 500 mA 12 V  75% standby — 12 V  500 mA

As shown in Table 5, the device control table may manage the Session ID,company ID, Product ID, Load Characteristic, Current Characteristic,Voltage characteristic, Efficiency Characteristic, StatusCharacteristic, input voltage at the input end of the DC-to-DCconverter, output voltage and output current at the output end of theDC-to-DC converter of the wireless power receiver, etc. The statuscharacteristic provides information about whether the wireless powerreceiver is completely charged and in standby mode, is insufficientlycharged and in standby mode, is being charged in a Constant Voltage (CV)mode, or is being charged in Constant Current (CC) mode.

The wireless power transmitter transmits a signal to respond to therequest for searching for a wireless power transmitter (hereinafter,referred to as a “response search signal”) to the wireless powerreceiver in response to the search signal, in step S622. For example,the response search signal may have a data structure as shown in Table 6below.

TABLE 6 Frame Type Reserved Sequence Number Network ID Response Search 4bits 1 byte 1 byte

In Table 6, the Frame Type field indicates a type of the signal, i.e., aresponse search signal. The Reserved field is reserved for later use,and assigned 4 bits. The Sequence Number field indicates a sequentialorder of the corresponding signal, and is assigned 1 byte. For example,the sequential order of the Sequence Number may be incremented by 1 foreach signal transmission or reception.

The Network ID field indicates a network identifier of the wirelesspower transmitter, and is assigned 1 byte.

The wireless power receiver transmits a signal to the wireless powertransmitter to request subscription to a wireless powertransmitting/receiving network (hereinafter, referred to as a “requestjoin” signal), in step S623. For example, the request join signal mayhave a data structure as shown in Table 7.

TABLE 7 Frame Sequence Network Product Input Input Typical Typical powerType Reserved Number ID ID Voltage MIN Voltage MAX Output Voltage OutputCurrent impedance consumption Request 4 bit 1 Byte 1 Byte 4 Byte 1 Byte1 Byte 1 Byte 1 Byte 4 bit 4 bit join

In Table 7, the Frame Type field indicates a type of the signal, i.e., arequest join signal. The Reserved field is reserved for later use, andis assigned 4 bits. The Sequence Number field indicates a sequentialorder of the corresponding signal, and is assigned 1 byte. For example,the sequential order of the Sequence Number may be incremented by 1 foreach signal transmission or reception.

The Network ID field indicates a network identifier of the wirelesspower transmitter, and is assigned 1 byte. The Product ID field hasproduct information of the wireless power receiver, which includesserial number information. The Input Voltage MIN field indicates aminimum voltage applied at the input end of the DC-to-DC converter (notshown) of the wireless power receiver, and is assigned 1 byte.

The Input Voltage MAX field indicates a maximum voltage applied at theinput end of the DC-to-DC converter (not shown) of the wireless powerreceiver, and is assigned 1 byte. The Typical Output Voltage fieldindicates a rated voltage applied at the output end of the DC-to-DCconverter of the wireless power receiver, and is assigned 1 byte. TheTypical Output Current field indicates a rated current passing throughthe output end of the DC-to-DC converter of the wireless power receiver,and is assigned 1 byte.

The Impedance field has impedance information of the wireless powerreceiver, and is assigned 4 bits. In the Impedance field, impedanceinformation of the receiving resonator may be written. Further, each ora sum of power loss (PRX-COIL) in the receiving resonator, power loss(PINDUCTION) due to the mutual inductance of the transmitting resonatorand the receiving resonator, power loss (PREC) in a rectifier of thewireless power receiver may be written in the Power Consumption field.Additionally, voltage and current at the input end of the DC-to-DCconverter of the wireless power receiver may also be written in thePower Consumption field.

The wireless power transmitter may determine whether to subscribe thedetected wireless power receiver to the wireless power network based onthe received request join signal. For example, the wireless powertransmitter may determine whether to subscribe the wireless powerreceiver to the wireless power network based on the device control tableshown in Table 4. The wireless power transmitter may deny thesubscription of the wireless power receiver, if power requested by thewireless power receiver is higher than power that can be supplied by thewireless power transmitter.

Having determined to subscribe the wireless power receiver to thewireless power network, the wireless power transmitter may assign thewireless power receiver a session ID. The wireless power transmitter maygenerate a signal to respond to the request join signal (hereinafter,referred to as a “response join signal”) including the session ID orinformation about whether to subscribe the wireless power receiver tothe wireless power network. In step S624, the wireless power transmittertransmits the response join signal to the wireless power receiver.

For example, the response join signal may have a data structure as shownin Table 8.

TABLE 8 Frame Sequence Network Session Type Reserved Number IDPermission ID Response 4 bits 1 byte 1 byte 4 bits 4 bits Join

In Table 8, the Frame Type field indicates a type of the signal, i.e., aresponse join signal. The Reserved field is reserved for later use, andis assigned 4 bits. The Sequence Number field indicates a sequentialorder of the corresponding signal, and is assigned 1 byte. For example,the sequential order of the Sequence Number may be incremented by 1 foreach signal transmission or reception.

The Network ID field indicates a network identifier of the wirelesspower transmitter, and is assigned 1 byte. The Permission fieldindicates whether the wireless power receiver is permitted to subscribeto the wireless power network, and is assigned 4 bits. For example, avalue ‘1’ in the Permission field indicates that subscription of thewireless power receiver is permitted, while a value ‘0’ in thePermission field indicates that subscription of the wireless powerreceiver is not permitted. The Session ID field indicates an identifierof a session assigned by the wireless power transmitter to the wirelesspower receiver for the wireless power transmitter to control thewireless power network. The Session ID field is assigned 4 bits.

The wireless power receiver 650 transmits an ACK signal in response tothe response signal, in step S625.

FIG. 7 illustrates a method of detecting a relatively small wirelesspower receiver, according to an embodiment of the present invention.

Referring to FIG. 7, a wireless power receiver 660 is placed over thewireless power transmitter 600 while the second detection power 613 isapplied. However, it is assumed that the wireless power transmitter 600does not detect a load change with the second detection power 613. Thus,the wireless power transmitter 600 does not immediately detect thewireless power receiver 660.

The wireless power transmitter 600 then applies a first detection power640 for a new period of time. The wireless power transmitter 600 detectsthe load change with the first detection power 640 and detects thewireless power receiver 660 based on the load change. Thereafter, thewireless power transmitter 600 keeps applying the first detection power640. The wireless power receiver 660 receives the first detection power640 and transmits the search signal based on the first detection power640, in step S651. In step S652, the wireless power transmitter 600transmits the response search signal in response to the search signal.The wireless power receiver 660 transmits the request join signal instep S653, and the wireless power transmitter 600 transmits the responsejoin signal in step S654. In step S655, the wireless power receiver 660transmits the ACK signal.

FIG. 8 is a flowchart illustrating a method of controlling a wirelesspower transmitter, according to an embodiment of the present invention.

Referring to FIG. 8, the wireless power transmitter applies a firstdetection power for a first period of time, in step S801. The firstdetection power is strong enough to drive the wireless power receiverand enable the wireless communication unit to communicate. The firstdetection power may be applied for a time during which the wirelesspower receiver is driven and communicating.

In step S803, the wireless power transmitter determines whether thewireless power receiver is detected, while the first detection power isapplied. If the wireless power transmitter detects the wireless powerreceiver in step S803, the wireless power transmitter keeps applying thefirst detection power in step S805.

However, if the wireless power transmitter fails to detect the wirelesspower receiver in step S803, the wireless power transmitter may apply asecond detection power during a second period of time in step S807. Eachof the second detection powers are lower than the first detection power,but still have sufficient power to detect a wireless power receiver.Alternatively, the second detection power may be applied for a timerequired to increase voltage to reach the second detection power andthen to drop the voltage. As illustrated in FIGS. 6 and 7, the seconddetection powers may be applied with a predetermined gap between eachother.

In step S809, the wireless power transmitter determines if a wirelesspower receiver is detected, based on the second detection power. If thewireless power transmitter fails to detect the wireless power receiverin step S809, the wireless power transmitter applies the first detectionpower again during a new period of time, in step S801. However, when thewireless power receiver is detected in step S809, the wireless powertransmitter applies driving power in step S811. The driving power ishigh enough to drive the wireless power receiver and enable the wirelesspower receiver to communicate. The driving power has a higher level thanthe second detection powers.

FIG. 9 illustrates a method of detecting a wireless power receiver,according to an embodiment of the present invention.

Referring to FIG. 9, a wireless power transmitter 900 applies differentdetection powers during a predetermined cycle (referred to herein as an“adaptive cycle”). Specifically, the wireless power transmitter 900applies first detection power 901 for a time of K ms and then appliessecond detection powers 902 to 907.

The first detection power 901 is strong enough to detect a load changewith respect to a wireless power receiver that has a relatively lowconsumption power, and may be applied for a minimum period of time todetect the wireless power receiver. Alternatively, the first detectionpower 901 may be applied for a time required to increase voltage toreach the first detection power and then to drop the voltage back.

After applying the first detection power 901, the wireless powertransmitter 900 applies the second detection powers 902 to 907. Thewireless power transmitter 900 applies the second detection powers 902to 907 within a period of N ms. Each of the second detection powers 902to 907 has a duration of K ms. That is, each of the second detectionpowers 902 to 907 may have the same application time as that of thefirst detection power 901. Further, each of the second detection powers902 to 907 may be a minimum power to detect a wireless power receiverthat has relatively high consumption power.

When the adaptive cycle M ms is over, the wireless power transmitter 900applies first detection power 911 again. After applying the firstdetection power 911, the wireless power transmitter 900 applies thesecond detection powers 912 to 917.

In FIG. 9, a wireless power receiver 950 is placed over the wirelesspower transmitter 900, after application of the second detection power915 is completed, in step S916. The wireless power receiver 950 may havea relatively high consumption power.

While applying the second detection power 917, the wireless powertransmitter 900 detects a load change with respect to the wireless powerreceiver 950, and in turn, detects the wireless power receiver 950 basedon the load change. Having detected the wireless power receiver 950, thewireless power transmitter 900 applies driving power 928.

While applying the driving power 928, the wireless power receiver 950transmits the search signal, in step S921. In step S922, the wirelesspower transmitter 900 transmits the response search signal in responseto the search signal. The wireless power receiver 950 transmits therequest join signal in step S923, and the wireless power transmitter 900transmits the response join signal in step S924. In step S925, thewireless power receiver 950 transmits the ACK signal.

FIG. 10 illustrates method of detecting a relatively small wirelesspower receiver, according to an embodiment of the present invention. InFIG. 10, a wireless power receiver 960 is placed over the wireless powertransmitter 900 between application of the second detection power 912and the second detection power 913.

However, the wireless power transmitter 900 may not detect a load changewith the second detection power 913. Thus, the wireless powertransmitter 900 may not detect the wireless power receiver 960 and willapply the first detection power 931 for a new period of time.

The wireless power transmitter 900 detects the load change with thefirst detection power 931 and detects the wireless power receiver 960based on the load change. Having determined that the wireless powerreceiver 960 is nearby, the wireless power transmitter 900 appliesdriving power 940, which is received by the wireless power receiver 960.

In step S941, the wireless power receiver 960 transmits the searchsignal based on the driving power 940. In step S942, the wireless powertransmitter 900 transmits the response search signal in response to thesearch signal. The wireless power receiver 960 transmits the requestjoin signal in step S943, and the wireless power transmitter 900transmits the response join signal in step S944. In step S945, thewireless power receiver 960 transmits the ACK signal.

FIG. 11 is a flowchart illustrating a method of controlling a wirelesspower transmitter, according to an embodiment of the present invention.

Referring to FIG. 11, the wireless power transmitter applies a firstdetection power for a first period of time, in step S1101. The firstdetection power is sufficient for detecting a wireless power receiverwhose consumption power is relatively low and may be applied for aminimum period of time to detect a wireless power receiver.Alternatively, the first detection power may be applied for a timerequired to increase voltage to reach the first detection power and thento drop the voltage back.

The wireless power transmitter determines whether a wireless powerreceiver is detected while the first detection power is applied, in stepS1103. If the wireless power transmitter detects the wireless powerreceiver in step S1103, the wireless power stops applying the firstdetection power and applies driving power in step S1111.

However, if the wireless power transmitter fails to detect the wirelesspower receiver in step S1103, the wireless power transmitter may applythe second detection power during a second period of time, in stepS1107. Each of the second detection powers may have minimum power todetect the wireless power receiver that has relatively high consumptionpower. The second detection powers may be applied for a minimum periodof time to detect a wireless power receiver.

Alternatively, the second detection power may be applied for a timerequired to increase voltage to reach the second detection power andthen to drop the voltage back. The second detection power may be appliedwith a predetermined gap between each other.

The wireless power transmitter may detect the wireless power receiverbased on the second detection power, in step S1109. If the wirelesspower transmitter fails to detect the wireless power receiver in stepS1109, the wireless power transmitter applies the first detection poweragain during a new period of time, in step S1101. However, havingdetected the wireless power receiver in step S1109, the wireless powertransmitter applies driving power in step S1111. The driving powerdrives the wireless power receiver and enables the wireless powerreceiver to communicate. The driving power is higher than the seconddetection powers.

FIG. 12 illustrates a method of detecting a wireless power receiver,according to an embodiment of the present invention.

Referring to FIG. 12, a wireless power transmitter 1200 appliesdifferent detection powers during a predetermined cycle (referred toherein as an “adaptive cycle”). For example, the wireless powertransmitter 1200 applies different detection powers with three differentpower levels, i.e., a first detection power, a second detection power,and a third detection power. The first detection power has a minimumpower that can detect a wireless power receiver in a third category. Thesecond detection power has a minimum power level that can detect awireless power receiver in a second category. The third detection powermay have a minimum power level that can detect a wireless power receiverin a first category. The first to third categories are criteria fordistinguishing different consumption powers, reception powers, or sizesof the wireless power receivers.

For example, a wireless power receiver in the third category has ahigher power consumption, higher reception power, or greater size than awireless power receiver in the first category. Thus, the third detectionpower may have higher power consumption power, higher reception power,or a greater size than the first detection power because the lower thepower consumption of the wireless power receiver is, the higher thepower level required for detection is.

Table 9 illustrates such categories.

TABLE 9 Result of Survey Typical Expected Rx Rx Classification(Tentative) Device Charge Power Resonator Size Z-gap Category OutputPower BT Ear Set 0.42 W 10 × 10 mm² 5 mm #1 Po ≤ 1 W Eye Glasses 0.42 W30 × 50 mm² 15 mm  for 3D TV Smart Remote 1.995 W 40 × 70 mm² 3 mm #2Controller Digital Still 1.995 W 8 × 50 mm² 5 mm 1 W < Po ≤ 3 W CameraNintendo DS 2 W 40 × 70 mm² 3 mm Smart Phone 4 W 40 × 70 mm² 3 mm #3 3 W< Po ≤ 6 W iPhone4 4 W 40 × 70 mm² 4 mm Galaxy Tab 7 7 W 60 × 120 mm² 4mm #4 New Galaxy 8-10 W 120 × 120 mm² 4 mm 6 W < Po ≤ 12 W Tabs iPad210.5 W 120 × 120 mm² 4 mm 12 W < Po ≤ TBD

The wireless power transmitter 1200 applies different detection powers,e.g., the first to third detection powers, to detect a differentlycategorized wireless power receiver within a predetermined period oftime.

In FIG. 12, a wireless power receiver 1250 is placed over the wirelesspower transmitter 1250 between the application of the second detectionpowers 1208 and 1209. The wireless power receiver 1250 belongs to thefirst category.

While applying the second detection power 1209, the wireless powertransmitter 1200 may not detect the wireless power receiver 1250. Also,while applying the second detection power 1210, the wireless powertransmitter 1200 may not detect the wireless power receiver 1250. Thewireless power transmitter 1200 may detect a load change with the thirddetection power 1211. The wireless power transmitter 1200 detects thewireless power receiver 1250 in the first category based on the loadchange, and then stops applying the third power 1211 and applies drivingpower 1220.

In step S1231, the wireless power receiver 1250 transmits the searchsignal, based on the driving power 1220. The wireless power transmitter1200 transmits the response search signal in response to the searchsignal in step S1232. The wireless power receiver 1250 transmits therequest join signal in step S1233, and the wireless power transmitter1200 transmits the response join signal in step S1234. In step S1235,the wireless power receiver 1250 transmits the ACK signal.

However, if the wireless power receiver belongs to the second category,the wireless power transmitter 1200 detects the wireless power receiverin the second category during the application of the second detectionpower or the application of the third detection power.

Alternatively, if the wireless power receiver belongs to the thirdcategory, the wireless power transmitter 1200 detects the wireless powerreceiver in the second category during the application of the firstdetection power, the application of the second detection power, or theapplication of the third detection power.

FIGS. 13A to 13C are diagrams illustrating detected power applied by awireless power transmitter, according to various embodiments of thepresent invention. Specifically, the wireless power transmitter is in afirst class in FIG. 13A, in a second class in FIG. 13B, and in a thirdclass in FIG. 13C.

Referring to FIG. 13A, the wireless power transmitter applies the firstto third detection powers within a predetermined period T. The differentdetection powers with the three different power levels are classifiedinto a first detection power, a second detection power, and a thirddetection power. The first detection power has a minimum power levelthat will detect a wireless power receiver in the third category, andthe second detection power has a minimum power level that will detect awireless power receiver in the second category, and the third detectionpower has a minimum power level that will detect a wireless powerreceiver in a first category.

In FIG. 13A, the wireless power transmitter sequentially applies thefirst to third detection powers 1301, 1302, and 1303 in an increasingdirection of power level within the predetermined period T.Alternatively, more or fewer detection powers may be applied. The firstto third detection power may also be applied differently, e.g.,randomly, than illustrated in FIG. 13A. The first to third detectionpower 1304, 1305, and 1306 may also be applied repeatedly.

Referring to FIG. 13B, the wireless power transmitter applies the firstto fourth detection powers within the predetermined period T. Asdescribed above, the wireless power transmitter is a second-classwireless power transmitter, and charges a wireless power receiverbelonging to any of first to fourth categories. The different detectionpower with four different power levels may be classified into a firstdetection power, a second detection power, a third detection power, anda fourth detection power. The first detection power has a minimum powerlevel that will detect a wireless power receiver in a fourth category,the second detection power has a minimum power level that will detect awireless power receiver in a third category, the third detection powerhas a minimum power level that will detect a wireless power receiver ina second category, and the fourth detection power has a minimum powerlevel that will detect a wireless power receiver in a first category.

In FIG. 13B, the wireless power transmitter sequentially applies thefirst to fourth detection powers 1311, 1312, 1313, and 1314 in anincreasing direction of power level within the predetermined period T.Alternatively, more or fewer detection powers may be applied. The firstto fourth detection power may also be applied differently, e.g.,randomly, than illustrated in FIG. 13B. The first to fourth detectionpower 1315, 1316, 1317, and 1318 may also be applied repeatedly.

Referring to FIG. 13C, the wireless power transmitter applies the firstto fifth detection powers within the predetermined period T. Asdescribed above, the wireless power transmitter is a third-classwireless power transmitter, and charges a wireless power receiverbelonging to any of first to fifth categories. The different detectionpowers with five different power levels are classified into a firstdetection power, a second detection power, a third detection power, afourth detection power, and a fifth detection power. The first detectionpower has a minimum power level that will detect a wireless powerreceiver in the fifth category, the second detection power has a minimumpower level that will detect a wireless power receiver in the fourthcategory, the third detection power has a minimum power level that willdetect a wireless power receiver in the third category, the fourthdetection power has a minimum power level that will detect a wirelesspower receiver in the second category, and the fifth detection power hasa minimum power level that will detect a wireless power receiver in thefirst category.

In FIG. 13C, the wireless power transmitter sequentially applies thefirst to fifth detection powers 1321, 1322, 1323, 1324, and 1325 in anincreasing direction of power level within the predetermined period T.Alternatively, more or fewer detection powers may be applied. The firstto fifth detection powers may also be applied differently, e.g.,randomly, than illustrated in FIG. 13C. The first to fifth detectionpower 1326, 1327, 1328, 1329, and 1330 may also be applied repeatedly.

According to various embodiments of the present invention, aconfiguration and process of detecting a wireless power receiver isprovided by the wireless power transmitter. Furthermore, according tothe embodiments of the present invention, the wireless power receivermay be detected in a more efficient and reliable manner, therebypreventing power waste.

While the present invention has been particularly shown and describedwith reference to certain embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims and theirequivalents.

What is claimed is:
 1. A method for wirelessly transmitting power to awireless power receiver by a wireless power transmitter, the methodcomprising: periodically outputting a power sequence comprising a firstdetection power and a second detection power through a resonator of thewireless power transmitter, wherein a level of the first detection poweris greater that a level of the second detection power; detecting achange of a load impedance while outputting the power sequence; based ondetecting the change of the load impedance, stopping outputting of thepower sequence, wherein the change of the load impedance is caused byplacement of the wireless power receiver near the wireless powertransmitter; and after stopping outputting of the power sequence,outputting a driving power for driving a controller of the wirelesspower receiver.
 2. The method of claim 1, wherein detecting the changeof the load impedance comprises: identifying the change of the loadimpedance exceeding a predetermined threshold; and detecting thewireless power receiver based on the change of the load impedanceexceeding the predetermined threshold.
 3. The method of claim 1, whereinthe power sequence further comprises a third detection power which issufficient to drive the controller of the wireless power receiver. 4.The method of claim 3, wherein the first detection power and the seconddetection power is outputted for a first duration and the thirddetection power is outputted for a second duration, and wherein thesecond duration is long enough to drive the controller of the wirelesspower receiver.
 5. The method of claim 4, wherein the second duration islonger than the first duration.
 6. The method of claim 1, wherein thelevel of the second detection power is a minimum power level that willdetect the change of the load impedance with respect to the wirelesspower receiver in a first category.
 7. The method of claim 1, whereinthe second detection power is outputted after a predetermined time gapafter outputting the first detection power.
 8. The method of claim 3,wherein outputting the driving power comprises continually outputtingthe third detection power when the wireless power receiver is detectedwhile the third detection power is outputted.
 9. The method of claim 1,wherein outputting the driving power comprises increasing one of thefirst detection power and the second detection power to a powersufficient to drive the controller of the wireless power receiver.
 10. Awireless power transmitter for transmitting power to a wireless powerreceiver, the wireless power transmitter comprising: a resonator fortransmitting power to the wireless power receiver, and a controllerconfigured to: periodically output a power sequence comprising a firstdetection power and a second detection power through the resonator,wherein a level of the first detection power is greater that a level ofthe second detection power; detect a change of a load impedance whileoutputting the power sequence; based on detecting the change of the loadimpedance, stop outputting of the power sequence, wherein the change ofthe load impedance is caused by placement of the wireless power receivernear the wireless power transmitter; and after stopping outputting ofthe power sequence, output a driving power for driving a controller ofthe wireless power receiver.
 11. The wireless power transmitter of claim10, wherein the controller identifies the change of the load impedanceexceeding a predetermined threshold, and detect the wireless powerreceiver based on the change of the load impedance exceeding thepredetermined threshold.
 12. The wireless power transmitter of claim 10,wherein the power sequence further comprises a third detection powerwhich is sufficient to drive the controller of the wireless powerreceiver.
 13. The wireless power transmitter of claim 12, wherein thefirst detection power and the second detection power is outputted for afirst duration and the third detection power is outputted for a secondduration, and wherein the second duration is long enough to drive thecontroller of the wireless power receiver.
 14. The wireless powertransmitter of claim 13, wherein the second duration is longer than thefirst duration.
 15. The wireless power transmitter of claim 10, whereinthe level of the second detection power is a minimum power level thatwill detect the change of the load impedance with respect to thewireless power receiver in a first category.
 16. The wireless powertransmitter of claim 10, wherein the second detection power is outputtedafter a predetermined time gap after outputting the first detectionpower.
 17. The wireless power transmitter of claim 12, wherein thecontroller continually outputs the third detection power when thewireless power receiver is detected while the third detection power isoutputted.
 18. The wireless power transmitter of claim 10, wherein thecontroller increases one of the first detection power and the seconddetection power to a power sufficient to drive the controller of thewireless power receiver.